Digital circuit providing a trigger signal to trigger an event based on operating functions of moving apparatus elements, particularly to trigger an ignition pulse in an internal combustion engine

ABSTRACT

A first transducer provides a sequence of pulses, for example speed-dependent pulses, which cause, sequentially, loading and unloading of more rapidly occurring count pulses. The count pulses may have a count repetition rate depending on an operating condition of the device, for example loading on the engine as determined by inlet manifold vacuum, or fuel/air flow to the engine. The binary number of the count pulses, in a certain interval as determined by the speed or tachometer pulses is compared with the binary number developed, non-linearly, from the function generator as the engine rotates and, upon coincidence of count numbers, a pulse is generated which triggers the ignition of the engine, thereby providing for good approximation of the non-linear spark advance/retard timing with respect to engine speed and loading.

7 United States Patent Stark 1 Dec. 2, 1975 1 1 DIGITAL CIRCUITPROVIDING A 3,749,073 7/1973 Asplund 123/117 R TRIGGER SIGNAL T0 TRIGGERAN EVENT P arner BASED ON OPERATING FUNCTIONS OF 3,832,981 9/1974Wakamatsu et al 123/32 EA MOVING APPARATUS ELEMENTS, PARTICULARLY TOTRIGGER AN IGNITION PULSE IN AN INTERNAL COMBUSTION ENGINE [75]Inventor: Eberhard Stark, Korntal, Germany [73] Assignee: Robert BoschG.m.b.H.,

Gerlingen-Schillerhoehe, Germany [22] Filed: Aug. 12, 1974 [211 App].No.: 496,651

[30] Foreign Application Priority Data Sept. 14, 1973 Germany 2346333[52] US. Cl. 123/117 R; 123/117 D [51] Int. Cl. F02P 3/02 [58] Field ofSearch 123/117 R, 32 EA [56] References Cited UNITED STATES PATENTS3,454,871 7/1969 Nolting 123/117 R 3,592,178 7/1971 Schiff 123/117 R3,738,339 6/1973 Huntzinger et al. 123/117 R Primary ExaminerCharles J.Myhre Assistant Examiner.1oseph A. Cangelosi Attorney, Agent, orFirm-Flynn & Frishauf [57] ABSTRACT A first transducer provides asequence of pulses, for example speed-dependent pulses, which cause,sequentially, loading and unloading of more rapidly occurring countpulses. The count pulses may have a count repetition rate depending onan operating condition of the device, for example loading on the engineas determined by inlet manifold vacuum, or fuel/air flow to the engine.The binary number of the count pulses, in a certain interval asdetermined by the speed or tachometer pulses is compared with the binarynumber developed, non-linearly, from the function generator as theengine rotates and, upon coincidence of count numbers, a pulse isgenerated which triggers the ignition of the engine, thereby providingfor good approximation of the non-linear spark advance/retard timingwith respect to engine speed and loading.

27 Claims, 7 Drawing Figures STARTER LlNE START NUMBER STORE ROM] OSCILLATOR 1 2 21 22 3 I INDUCTION 26 vA c uuM SENSOR 29 l STORAGE I asREFERENCE COUNTER I FULSESWRCE 111m,

37 FUNCTION BINARY GENERATOR J COMPARATOR 1 314 L0 ll 33 FUNCTTII 1|PULSE DOWN L I z COUNTER L 1 WAVE 32 SHAPER l l l 202 START NUMBER 66 ASTORE-ROM 2 TURE 7 l.i \LL SENSOR THRESHOLD SWITCH UISQ Patem Dec. 2,1975 Sheet 1 of4 3,923,021

g 1 1.9 ExHAUST COMPOSITON SPEED PULSE WAVE CONTROL LINE TRANSDUCERSHAPER IIJIO 1 14 c STARTER LINE I 1-7 -I;---- I j I ,K

I I I 16 L8 19 IL I g I ZII$385I 20 II IIIII Z I OSCILLATORFLINSTANTANEOUS I ENGINE SPEED 27 I DOWN COUNTER IND CTION 3 25 E5 IVA3C8UUM SENSOR 29 STORAGE I/ COUNTER 3s REFERENCE fi PULSE SOURCE I IIfFUNCTION BINARY {l 37 GENERATOR l COMPARATOR 33 3 II I I I II H EI J I IE ES OWN I wAvE/ 32 SHAPER I I I I I IT START NUMBER L2 ENGINE STORE-ROM 2 N TEMPERA- TURE L7 5/ u M, SENSOR THRESHOLD SWITCH Dec. 2, 1975Sheet 3 of4 3,923,021

U.S. Patent Dec. 2, 1975 Sheet4 0f4 3,923,021

Fig-7 loT DIGITAL CIRCUIT PROVIDING A TRIGGER SIGNAL TO TRIGGER AN EVENTBASED ON OPERATING FUNCTIONS OF MOVING APPARATUS ELEMENTS, PARTICULARLYTO TRIGGER AN IGNITION PULSE IN AN INTERNAL COMBUSTION ENGINE Thepresent invention relates to a digital system to provide a trigger pulseto trigger an operating event in an apparatus, and more particularly totrigger the ignition instant in an internal combustion engine, in whichthe particular instant of time, with respect to crankshaft position (orother movable element positions of the device) is accuratelypredetermined.

The ignition timing, that is, the advance or retard angle of ignitionwith respect to speed and load on the engine, must be changed as thespeed and load on the engine, respectively, change; other operating orambient parameters may, additionally, have to be taken intoconsideration. Changing the ignition instant is required by the timetaken for the combustible mixture to burn. Upon a spark being generatedat the gap of the spark plug, only that portion of the combustibleair-fuel mixture in the cylinder will ignite which is in immediatevicinity of the spark plug gap. A flame front or wall then passes, withapproximately constant speed, throughout the cylinder and ignites theremainder of the combustible mixture therein. This flame front,, ormovable wall of flame, requires roughly the same time to pass from thespark plug to the cylinder wall regardless of the speed of the engine.

Maximum combustion pressure should occur in the engine shortly after thepiston passes through the upper dead center (UDC) position thereof. Thiscondition, then, requires adjustment of the timing of the ignition sparkwith respect-to the angular position of the crankshaft of the piston inthe respective cylinder in such a manner that the spark is advanced fromUDC position as the speed of the machine increases, in order tocompensate for the constant propagation time of the flame front in thecylinder upon combustion.

The speed of the flame front depends on the composition of thecombustible mixture within the cylinder, that is, on the relativemixture of fuel and air, with respect to stoichiometric values. If theload on the internal combustion is high, and the throttle thereto iswide open so that the inlet manifold will have a low vacuum therein, thecylinder will receive a rich mixture which is readily ignitable. Theflame front will propagate with high speed in a rich mixture. Ignitionmay therefore be retarded. If, however, the loading on the engine isonly small and the throttle is essentially closed, the mixture suppliedby a carburetor will be on the lean side, which results in a lowerpropagation speed of the flame front. This condition, then, requiresignition advance. In general, reference is made in this connection tospark advance if the angle ofignition, with respect to crankshaft angle,is well in advance of UDC position; the spark is retarded if the angleof ignition is only slightly in advance of UDC position of the piston,or at, or even after, or behind the UDC position.

The pressure or, rather, the vacuum in the inlet manifold customarily isused as a measure for the load on the internal combustion engine. Thisvacuum can be measured by means of a diaphragm chamber. Speed of theengine is customarily measured in mechanical ignition control systems bymeans of centrifugal weights.

Various electronic circuits have been proposed in which the customarymechanical change of angular position of the ignition angle is replacedby electronic circuitry; such electronic circuitry operates without wearand tear. Most such circuits use analog technology. Speed of the engineand inlet vacuum are transformed into d-c voltages of variableamplitude. While satisfactory in many respects, analog technology hasthe disadvantage that ignition timing circuits require extensiveadjustment before the timing circuits can be matched to an engine, andto match the various voltage levels of the various stages of the circuitto each other. Stray fields and possible feedback within the variouscomponents of such circuits have to be compensated for. Long-termvariations in analog circuits also occur, causing drift, so that thevoltage levels of signals in the circuit may slightly shift due to agingof the components in the circuits used.

It has previously been proposed to use digital circuits to adjust andchange the ignition angle, in which the speed of the internal combustionengine is sensed by counting in a counter the output pulses from atachometer generator during a predetermined time. The time itself,during which the pulses are counted, is determined by a monostablemultivibrator or flip-flop (FF). The pulse duration, that is, theunstable time of the monostable FF is changed in dependence on inletmanifold vacuum, and may, additionally, be changed in dependence onother operating parameters. This type of circuit is only partially adigital circuit; the monostable FF, providing a predetermined timingperiod, is actually an analog component which has the disadvantagesabove. referred to of analog circuitry. lt is, additionally, difficultto control monostable FFs by more than one operating parameter toaccurately determine the unstable time thereof.

Circuits of this type, which may be termed composite or semi-digitalcircuits determine the ignition angle by means of a counting procedurewhich is sub-divided into two parts or sections. The first sectionstarts, for example, before UDC position. The output pulses of thetachometer generator are counted during the time fixed by the monostableFF. The counting stage increases, with increasing speed. Thereafter, ata predetermined angular position of the crankshaft, for example 45 inadvance of UDC position, the counting is continued and terminated at apredetermined time of count pulses, at which time the ignition system istriggered. If more pulses were counted during the first countingportion, then lesser numbers of pulses need be counted in the secondportion. As a result, ignition is advanced at high speed.

Such a counting system may introduce a dynamic error if the speed of theinternal combustion engine changes rapidly, since speed is determinedonly once for each revolution of the crankshaft of the engine. If theignition is then triggered after a subsequent half rotation of thecrankshaft, the then instantaneous speed of the engine may already havechanged substantially.

It is an object of the present invention to provide a system which isparticularly adapted to be useful to trigger an ignition event, andwhich is entirely based on digital technology, utilizes digitalcomponents, and which largely avoids dynamic errors. In general, such asystem can provide a pulse representative of a predetermined event independence on various parameters.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, a first transducer isprovided which supplies a sequence of pulses. This transducer may, forexample, be a speed signal transducer providing a sequence of pulsesrepresentative of engine speed. The time lapse, between pulses, providesa digital number which, as such, preferably is generated by anoscillator; the frequency of this oscillator, which generates pulseswhich will form a count number may, itself, be variable and controlledby an operating parameter of the engine, for example inlet manifoldvacuum. The oscillator will have a frequency which is a high multiple ofthe frequency of the speed pulse generator, and the count number,between pulses, will then be a binary number representative of speed.This number is stored in a storage counter.

A function generator is provided which provides a sequence of pulseswhich have a time distribution, with respect to a datum, which isrepresentative of the function of variation of an operating condition asthe machine operates, for example, of the function of ignition timingwith respect to angular crankshaft position. This function is non-linearand may, for example, be represented by non-linearly distributed marks,or teeth, on a rotating disk, or element, coupled to rotate with thecrankshaft of the engine. A second count number will thus be provided,and when the stored count, derived from the pulses of the oscillator andaccumulated during subsequent pulses of the speed transducer matches thecount number of the count derived from the function generator, a digitalcomparator provides an output signal indicative of such match, orequality, which output signal is then used to trigger an ignition event.

As applied to an internal combustion engine, the crankshaft of theengine thus drives two pulse sources, namely a pulse source which hasoutput pulses uniformly distributed, angularly, with respect to thecrankshaft; and a second pulse source, which operates as a functiongenerator, and which provides pulses in dependence on a desired speedcharacteristic with respect to crankshaft angle. The speed pulse source,or tachometer generator, may provide a high number of pulses for eachfull revolution of the crankshaft, so that dynamic errors in measuringspeed can be substantially reduced. Each new tachometer generator orspeed pulse provides new speed information to the counter, in digitalform. The function generator can be so arranged that any desireddistribution of speed with respect to ignition advance angle can besimulated, that is, can be matched to a particular internal combustionengine, or to a type of engine. The output derived from the functiongenerator will be a binary number, counted in a function counter whichwill have a number counted therein which is a measure of the crankshaftangle through which the crankshaft has rotated, after a certain datumlevel has been passed, that is, after the function generator has startedto provide pulses.

The circuit in accordance with the present invention permits a number ofpossibilities to further consider additional operating parameters inpure digital form. For example, the initial counting state of any one ofthe counters may be changed. A particularly simple possibility toconsider the vacuum in the inlet manifold is to change the operatingfrequency of the count oscillator,

for example by introducing a variable L/C circuit therein.

The invention will be described by way of example with reference to theaccompanying drawings, wherein:

FIG. 1 is a general schematic block circuit diagram of the system inaccordance with the present invention;

FIGS. 2-6 are graphs used in explanation of the operation of the circuitin accordance with FIG. 1; and

FIG. 7 is a schematic representation of'a combined optical speed andfunction generator transducer.

A tachometer generator 10, forming a speed-pulse transducer (FIG. 1) iscoupled to a rotating shaft 38 of an internal combustion engine (notshown), for example to the crankshaft, directly or by means of atransmission. Transducer 10 includes a star wheel 11 havingferromagnetic teeth which pass by a magnetic core 12, on which a coil 13is in inductively coupled relationship. A terminal of coil 13 isconnected to chassis or ground; the other terminal forms the output ofthe speed pulse transducer 10. A wave-shaping circuit 14 is connected tothe speed pulse transducer, including a differentiator 15 and a Schmitttrigger l6. Differentiator 15 has a differentiating capacitor 17 whichis connected to the output of tachometer generator 10 and has anotherterminal thereof connected to a resistor 18, which in turn is grounded.The junction of the capacitor 17 and resistor 18 is connected over adiode 19 to the Schmitt trigger 16.

A vacuum diaphragm chamber 20 is connected by means of piping or tubing21 to the inlet manifold of the internal combustion engine (not shown).A mechanical coupling 22 is connected to chamber 20 to change theposition of a ferrite core 23 within a high frequency coil 24. Coil 24,together with a capacitor 25 forms the tank circuit of an oscillator 26;the position of the core 23 within coil 24 determines the frequency ofoscillator 26.

The output of oscillator 26 is connected to the count input z of anengine speed counter 27. Counter 27, preferably, is a backward, or downcounter, which counts downwardly from a number which can be set therein.The load input 1 of the engine speed counter 27 is connected to theoutput of the Schmitt trigger l6. Pulses derived from the oscillator 26are thus counted when a pulse from Schmitt trigger 16 is received untilthe next pulse, again, is received as will appear in detail below. Thebinary count state of the engine speed counter 27 which, due to thenumber of teeth on star wheel 11 is partically an instantaneous speedcounter, is transferred to the input of a storage counter 28. Storagecounter 28 has a load input 1 which is energized over an inverter 29connected to the output of the Schmitt trigger 16.

A function generator 30 is connected to the crankshaft or similarrotating element of the engine 38, and, like the speed transducer 10,has a star wheel 31 which is driven from the engine. Star wheel 31 hasferromagnetic teeth which pass the core 32 as the star wheel rotates. Incontrast to the star wheel 11, on which the teeth are uniformlydistributed over the surface, wheel 31 has the teeth locatednonuniformly over the surface thereof. A coil 13 is wound over core 32,grounded at one end, and having its other terminal connected as theoutput of the function generator 30, directly to the input of a Schmitttrigger 34, which operates as a wave shaper.

The output of Schmitt trigger 34 is connected to the count input 2 of afunction pulse counter 35. Function pulse counter 35, preferably, is adown counter which counts downwardly from a predetermined value. Theload input 1 of the counter 35 is connected to the output of a referencepulse transducer or source, formed by a switch 36 which is periodicallyopened and closed by a cam 37 operating in synchronism with crankshaftrotation of the engine. Broken line 38 schematically indicates thesynchronous drive of the two star wheels 1 1, 31 and of cam 37 from thecrankshaft of the internal combustion engine. The binary output of thefunction counter 35 and the output of the storage counter 28 are bothconnected to two corresponding binary inputs of a binary comparator 39.The comparator 39 is connected to an amplifier 40, and provides anenergizing pulse thereto upon coincidence of binary count input from thetwo counters 28, 35.

Two start number, or initial state storage counters 41, 42 are provided,respectively connected to the instantaneous engine speed counter 27 andto the function pulse counter 35, respectively. The two start numberstorage counters may be read only memories (ROMs) and are, therefore,indicated as ROM-1 and ROM-2; addressing inputs 43, 44, respectively,connected to the counters 41, 42 permit addressing the counters withpredetermined numbers to be set therein. The various addressing inputs,collectively indicated as Za and Zb are connected to suitable inputsthereof.

The binary numbers Za and Zb are indicated, schematically, asthree-digit binary numbers. One digit of the binary number Zb isdetermined by the output signal of a threshold switch 45, the input ofwhich is connected to the tap point of a voltage divider formed by aresistor 46 and an NTC-resistor 47 which is a thermally responsiveresistor, in thermal contact with the engine block of the internalcombustion engine, to sense engine temperature.

One digit of the binary number Za is determined by whether the starterswitch 48 is opened or closed; starter switch 48 is connected to thestarter line. Another digit of the number Za is determined by the outputsignal derived from an exhaust gas sensor (not shown) and schematicallyindicated as switch 49, thus providing a binary signal on the exhaustcomposition control line. The other digits of the binary numbers Za andZb may be used, for example, for more accurate determination of theengine block temperature, so that the ignition timing can be adjusted,accurately, in various stages, depending on engine temperature. Otherparameters, such as ambient temperature, ambient air pressure, and thelike may also be considered and introduced as numbers into therespective start number storage counters 41, 42.

Basic operation: Alternating voltage pulses are induced in coil 13 oftachometer generator as the teeth of the star wheel 11 pass core 12. Thefrequency of these pulses is proportional to the speed of the internalcombustion engine, as transferred to wheel 11 by shaft 38. Thedifferentiator 15 provides steep needle pulses from the undulatingalternating voltage pulses of transducer 10; diode 19 passes only thepositive steep needle pulses to the Schmitt trigger 16, which transformsthese needle pulses into narrow square pulses, as shown. The pulseduration of these square pulses must be small with respect to the timegap between the square pulses.

The function generator also provides undulating voltage pulses which,however, need not be of such narrow width, nor so accurately triggered,so that the Schmitt trigger 34 can be connected directly to the outputof the coil 33; if desired, a differentiator similar to differentiator15 may also be interposed.

Oscillator 26 oscillates in accordance with the circuit parameters ofthe tank circuit formed of the inductance 24 and the capacitance ofcapacitor 25. It is an L/C oscillator connected, for example, as aHartley, or as a Colpitts oscillator. If the inlet manifold vacuum ishigh, that is, when the throttle is essentially closed, the diaphragmchamber 20 is compressed by the ambient air pressure, thus pulling theferrite core 23 by link 22 deeply into coil 24. This increases theinductivity of the coil 24 and the oscillation frequency of theoscillator 26 decreases. The oscillation frequency, thus, increases withdecrease in vacuum of the inlet manifold, and hence decreases withincreasing loading on the internal combustion engine.

The ferrite core 23, as shown in FIG. 1, is conical. This shape providesfor non-linear variation of the frequency with respect to change invacuum of the inlet manifold. By suitably shaping core 23, for exampleto be slightly bulged, or to be concave (with respect to a strictlyconical form) various vacuum-vs.-oscillator frequency characteristicscan be obtained.

Counters 27, 35, ROM'-l, and ROM-2, storage counter 28, and binarycomparator 39 are standard articles of commerce in the form ofintegrated components. Counters 27, 35 may, for example, be SN 74191;storage element 28 may be a SN 7475, and binary comparator 29 may be aSN 7485. The start number storage counters 41, 42 may, for example, beSN 7475 (similar to counter 28) if additional correction quantities Za,Zb are not needed, so that it will not have separate address inputs 43,44. If an initial count state should be considered, that is if,depending on operating conditions, different binary numbers Za, Zbshould be entered into the starting state of the counters 27 35, thenthe counters 41, 42 should be ROMs. If in order to test, or forexperimental circuits, or for other uses, the values in the memorycounters 41, 42, representative of the binary numbers Za, Zb are to bechanged, then a programmable read only memory (PROM) memory element suchas Intel 1702 is suitable.

The outputs of the memory counters 41, 42, whether fixed orprogrammable, provide a binary number, the value of which is determinedby the value of the binary number Za, Zb connected to the address inputthereof. The digital position of the output binary number can be matchedto the digital positions of the counters 27, 35.

Operation of the system as an ignition timing system, with reference toFIGS. 2-6: FIG. 2 illustrates the speed-timing adjustment curve 50 whichis obtained from mechanical ignition timing adjustment systems,operating by means of centrifugal weights. The ignition angle isindicated at az at the ordinate of FIG. 2. For ease of explanation, theabscissa has three scales; the upper scale indicates the speed n in rpm;the intermediate scale shows the speed nin revolutions per second, orHz; the third, and lower scale shows the time, T, necessary for onerevolution in milliseconds (ms). As can be seen from FIG. 2, theignition angle is effectively constant at low speeds up to about 1,000rpm; the angle then increases up to a speed of about 3,200 rpm at arather steep rate; above a speed of 3,200 rpm, the rate of increase isless.

The advance angle characteristic 51 of FIG. 3 is derived from the curve50 of FIG. 2. The ignition angle az is illustrated as a function of timeper revolution, or cycling time T, to a linear, increasing scale on theabscissa. As derived from FIG. 2, the characteristic should have aconstant value of about 10 above a cycling time of 60 ms. The circuitaccording to FIG. 1, however, provides for a gradual decrease as shownby the broken line 52. Such a gradual decrease is desirable since, atvery low speeds, the ignition angle should be shifted in the directionof spark delay. Centrifugal controllers cannot provide for suchincreasing spark delay since, at very low speeds, insufficientcentrifugal forces arise in the system.

The characteristic 51 or 52, in accordance with FIG. 3, is formed by thecircuit according to FIG. 1. The counter 27 counts a valuerepresentative of instantaneous engine speed, that is, the cycling timewhich elapses between two pulses from the speed pulse transducer 10.Angular adjustment of the ignition angle is thus referred to cyclingtime and not, as in the customary control systems, to the speed of theengine. The label instantaneous engine speed down counter given tocounter 27 is thus used only to conform to customary terminology; thecounter, actually, measures elapsed time of angular change of thecrankshaft or, in other words, the time gap between pulses derived fromthe transducer 10. The teeth of star wheel 11 are equally spaced aboutthe circumference thereof and thus, if the teeth are close together sothat the angle of rotation between teeth is very small, the counter 27will measure cycling time or, effectively, instantaneous engine speed.

FIGS. 4 and are graphs which illustrate how the cycling time counter, orinstantaneous speed counter 27 measures the time gap between pulses fromthe tachometer generator and, simultaneously, considers inlet manifoldvacuum.

The circuit of FIG. 1 is so polarized that the negative pulse flank.of apulse applied to the load input 1 of counter 27 (or of the storagecounter 28, respectively) causes transfer of the number applied to therespective binary number input. The count state of the counter 27 isthus transferred to the storage counter 28 as soon as Schmitt trigger 16provides a leading pulse edge which is inverted in the inverter 29. Thepulse from the trigger 16 is very short. Its trailing flank causes thebinary number Z01 stored in the start number store ROM-l 41 to betransferred to the instantaneous engine speed down counter 27. The countstate of the counter 27 is indicated by Z in FIG. 4. It starts at Z01and decreases in steps, since counter 27 is a down, or backward counter.

Tachometer generator 10 provides pulses at the time instants T1, T2, T3,T4 Assuming overall, average engine speed to remain constant initially,the time gap, that is, elapsed time between the first three pulses T1 toT3 remains constant. Let it be assumed that the speed increases, so thatthe pulse at time T4 occurs earlier, and so that the time gap isdecreased. The diagram according to FIG. 5 is drawn to the same scaleand the same speed relationships pertain. The difference between thediagram of FIGS. 4 and 5 is that the counting frequency in FIG. 5, asdetermined by the frequency of oscillator 26 is increased, since theloading on the engine has increased. As seen in FIG. 4, and at the lowercounting frequency, the counter 27 counts down from start count Z01 to arelatively high count state Z1 until the next pulse T2, T3 occurs. Thiscount number, Z1, is transferred to the storage counter 28, and counter27 is reset to its initial state Z01. At the fourth pulse T4, elapsedtime is shorter (the time gap is narrower) so that counter 27 will reachonly a still higher final state, or count Z3, which is transferred attime T4 into the storage counter 28.

The diagram of FIG. 5 illustrates, as noted, the same relationship at ahigher counting frequency. The counter, therefore, reaches a lower countstate Z2 after the first three pulses T1, T2, T3; at the fourth pulse,the count state Z4 is reached.

The final count state Z1 to Z4 is, therefore, on the one hand a measureof the elapsed time between subsequent pulses, that is, speed of theengine over the angular range between teeth of the star wheel 11 and,further, a measure of the pressure (or, rather, vacuum) in the inletmanifold. The determination of the ignition or firing angle a is derivedfrom a combination of the count state in the function pulse counter 35and the count state Z1 to Z4 reached by the counter 27, as illustratedin FIG. 6.

Counter 35 is set to an initial count state, as determined by startnumber store ROM-2 42 by the negative flank of the reference pulsesource 35, applied to terminal 1. FIG. 6 assumes that the counter 35 isloaded at an angle a0 of 42' in advance of UDC position. Functiongenerator 30 provides pulses starting at 40 in advance of UDC position.

In that region of the characteristic 51 (FIG. 3) which is steep, theangle az changes strongly at only small changes of cycling time, orsmall changes in instantaneous speed. Such large change in the ignitionangle az is obtained by spacing the teeth of the star wheel 31 furtherapart. Conversely, the teeth of the star wheel 31 must be very closetogether when the characteristic curve 51 (FIG. 3) is flat. The starwheel 31 (FIG. 1) schematically indicates by teeth distribution how thecurve of FIG. 3 can be formed. The first three teeth are relativelyclose together, since they have to generate a curve representative ofthe flat portion of curve 51 between T 10 ms and T 20 ms. Thereafter, asteeper portion follows and the teeth exhibit greater distance from eachother. They then become dense, again, in order to form the portion ofthe curve to T 60 ms, and then are very closely spaced since the curveshould be as flat as possible beyond T 60 ms.

The representation of the star wheel 31 (FIG. 1) is to be consideredonly schematically, since the teeth, there shown, are distributed overan angular range of more than in the example of FIG. 6, the teeth wouldbe present only in an angular range of from 40 to 10 before UDCposition, that is, should cover a range of only about 30. If a highangular resolution is required, the teeth 31 may be distributed over awide angular range as illustrated, for example, in FIG. 1 if anadditional transmission is used to rotate star wheel 31 faster than thecrankshaft.

The curve along which the count of counter 35 proceeds see FIG. 6 issteep in that portion where the characteristic of FIG. 3 is flat andvice versa. At high speeds, that is, in short cyclical periods T, thecounter 27 reaches count numbers which differ only slightly from theinitial count state Z01. In that range, the

count curve of the counter 35 is steep (see FIG. 6). The ignition angleaz changes only slightly when the change in cycling time is small, as isapparent from FIG. 3. The counting curve in accordance with FIG. 6reaches the count condition or state Z1 (FIG. 4) at an ignition angle azof about 18 in advance of UDC position. This is the instant of time inwhich the two binary numbers applied to the comparator 39 are equal, andcomparator 39 thus provides an output pulse, to be amplified in poweramplifier 40, to trigger the ignition system.

If the engine is highly loaded, that is, if the vacuum in the intakemanifold is low (curves of FIG. 5), a lower count will accumulate incounter 27, corresponding to count number Z2. The speed has not changed.Ignition only occurs when the count state, as derived from the countcurve of FIG. 6 has reached the count value Z2, that is, at an angle azof about 11 in advance of UDC. This is as desired since, as aboveexplained, at high loading the mixture introduced into the cylinder ismore readily flammable or ignitable, so that the time of ignition of theentire mixture is shorter.

The electromagnetic transducer and 30 may have the difficulty that theypermit only a limited resolution of the angles of the crankshaft, duringwhich ignition should be commanded. The circumference of a star wheel11, or 31, respectively, for tolerable size, may accomodate up to about120 teeth, or projections, spaced by an angular distance of about 3. Theaccuracy of resolution of the ignition angle az, in accordance with FIG.6, is determined by the distance of the teeth of the star wheel 31. Evenif a speed transmission of 1 4 is provided with respect to thecrankshaft, so that the star wheel 31 rotates four times as fast, andthe teeth are located as closely to each other as possible, an angularresolution of only about 0.8" can be obtained. The teeth of star wheel31 are spaced farther apart in the steeper ranges of the characteristiccurve of FIG. 3 so that in those ranges an angular resolution of about 5can be obtained. This resolution remains, independent of the lifetime,or use of the apparatus, and this constantly, perpetually availableresolution is a substantial advance with respect to mechanical ignitiontiming arrangements. Better accuracy should, however, be possible, andthe possibility to obtain high accuracy by digital circuits can beadditionally utilized by providing transducers which have even higherresolution. Instead of the electromagnetic transducers 10, 30,photoelectric transducers may be used. Such transducers are known. Alight source projects light to a photo cell; a disk is interposed in thepath of light between source and cell, the disk having transparent andopaque regions which alternate. Upon rotation of the disk, electricalvoltage pulses are generated in the photo cell. It is possible to applya high number of marks on disks of reasonable sizes, for example 1,2000opaque marks on the circumference of a disk customarily used in aphoto-electric transducer, for example of about 10 15 cm diameter. Theaccuracy of angular resolution can thus be increased by a factor ofabout 10 with respect to the resolution of an electromagnetictransducer.

A disk, for use in a photo-electric transducer and function generator isillustrated in FIG. 7. The disk rotates in the direction of the arrowabout a shaft 53'. It is formed with three tracks 54, 55, 56. The pathof light is directed transversely to the disk at the position shown bycircles 57, 58, 59 which, conjointly, represent an optical lightgenerating-receiving transducer system.

The arrangement of the markers on the disk will be explained withrespect to an eight-cylinder engine. The first, or inner track 54,cooperating with the optical transducer system 57 functions as areference pulse source and takes the position of the cam 37 and theswitch 36 of FIG. 1. The second, or intermediate track 55, together withphoto transducer system 58 forms the speed pulse transducer system, andreplaces system 10 of FIG. 1. The third track 54, together with thethird photo transducer system 59 forms the function generator,corresponding to generator 30 of FIG. 1.

The third track 56 is formed with two series of markers which take theposition of the teeth of the star wheel 31. Both series of markersextend over an angle somewhat greater than and are angularly stretchedwith respect to the counting characteristics of FIG. 6 by a factor oftwo. The disk of FIG. 7 thus rotate at twice the speed of the engine.For this reason, the first track 54 is formed with two referencemarkers, so that four reference pulses are provided to load counter 35.It provides four series of characteristic pulse sequences. Eachcrankshaft revolution provides four ignition pulses, as is required inan eight-cylinder engine. The two series of characteristic markers ofthe third track 57 may, of course, be distributed only about an angle ofabout 40 to 45, the disk then being driven directly from the crankshaft.Other transmission ratios, and angular distribution ranges of the diskmay likewise be used. The desired angular resolution available withdisks of predetermined size, and the number of cylinders of the enginehave to be considered.

The crankshaft positions are indicated in FIG. 7 where OT indicates therespective UDC positions, and the horizontal axis is representative ofthe 45 position with respect to UDC position.

Operation: Upon rotation, a reference pulse is provided by the firstreference track 54 at an angular crankshaft position of 45 in advance ofUDC position. This reference pulse provides for loading of the functionpulse counter 35 (FIG. 1) with the initial state or initial count numberZ02. At an angular position of about 43 in advance of UDC position, themarkers of the third track will pass before the transducer system 59 toprovide counting pulses for the function pulse down counter 35. Thedistance between markers follows the same functional relationship as thedistance of the teeth on star wheel 31. The markers continue beyond theupper dead center position. Such delayed ignition can be used at coldstarting. At very low temperatures of the engine block, NTC resistor 47(FIG. 1) may have such a high value that threshold switch 45, which is asimple Schmitt trigger, changes over and thus changes the binary numberZb entered at the address input 44 of the start number store 42. Thestart number store 42 then provides a binary number which issubstantially higher than Z02. The entire counting curve of FIG. 6 isshifted upwardly, resulting in a shifting of the ignition angle,regardless of speed, in the direction of spark retard. The shift of thecharacteristic curve of FIG. 6 may be so great that ignition angles azmay arise which are after the UDC position. The markers of the thirdtrack 56 are, therefore, continued beyond the UDC position.

In some special cases, it is desirable to shift the ignition in thedirection of spark retard during starting. The starter switch 48,connected to a starter line, is thus further connected to an addressinput 43 of the start number store ROM-1 41. When the starter switch 48is closed, the address input 43 will have an initial binary number Zaapplied thereto of such magnitude that the initial state Z01 of thecyclical, or instantaneous engine speed counter 27 is shifted to a lowervalue. This results, necessarily, in a lower counter state Z1 to Z4 (seeFIGS. 4 and 5). This lower final counter state of the counter 27, whichisthen transferred to storage counter 28 is reached only later bycounter 35, counting in accordance with the characteristics of FIG. 6.Thus, again, the angle of ignition is shifted towards retardation asdesired. Similarly, switch 49, controlled from an exhaust compositionsensor and inserted into an exhaust composition control line, may open,or close, to change the angle of ignition, as desired, in the directionof retardation, or spark advance. It is also possible to shift the angleof ignition in dependence on exhaust composition in steps, by utilizinga plurality of lines and switches corresponding to the switch 49 and thesingle exhaust composition control line, to set various initial numbersinto the start number store 41. Reference is made to U.S. Patentapplication Ser. No. 267,562, filed May 6, 1972, assigned to theassignee of the present invention, with respect to the effect ofchanging ignition timing on exhaust gas composition. Electricallyevaluating exhaust gas composition and deriving control signalstherefrom is described, for example, in U.S. Pat. No. 3,782,347,assigned to the assignee of the present application.

Various other changes and modifications may be made. For example,oscillator 26 may be constructed to have a fixed output frequency;loading on the engine is then sensed by selectively closing switchesconnected to suitable addressing control lines connected to therespective addressing inputs 43 or 44 of the start number storagememories 41, 42. Inlet manifold pressure then directly influences thebinary numbers Za and Zb, respectively, which control the initial countstate of counters 27 and 35, respectively. The total requirement ofcircuit components is somewhat less than when using an oscillator 26with variable frequency; vacuum in the inlet. manifold cannot, however,then be measured continuously but only in steps and some truncatingerror will result, depending upon the fineness of the steps with whichthe initial count numbers can be controlled. Rather than measuring thevacuum of the inlet manifold, flow of air to the engine, or flow of afuel-air mixture to the engine may also be measured, for example by asuitable air flow meter in the inlet manifold, such as a deflectableflap, disk, or the like which changes a slider position of apotentiometer, or contact positions of connecting lines respectivelyaddressing the start number stores 41, 42.

The frequency of oscillator 26, in the example of FIG. 1, may be placedin the order of about 100 kHz; it may shift, for example, between 80 to120 kHz. The angular distance of the markers on the disk in accordancewith FIG. 7 on the track 55, providing the cycling time (orinstantaneous speed) marks is preferably so selected that the oscillator26 provides about as many pulses, at center frequency, in the timebetween the occurrence of markers as there are, on the average, markerson the outer track 56. In the example of FIG.

7, the second track 55 has 16 markers. The disk, oper- 6 of 6,000 rpm,the time will be 0.3 ms. At an oscillator frequency of kHz, counter 27will count the time gaps, or elapsed time periods between markers to 300pulses at no-load speed, and will count 30 pulses at maximum speed. Theinitial count state Z01 of the counter 27 thus must be somewhat over300. A series of characteristic markers on the third, or outer track 56must then also have about 300 markers. This is readily obtainable withphotoelectric transducers of the scanned disk type.

A frequency divider may be connected to oscillator 26 if a smallernumber of markers are used for the track of the function generator, or alarger number of markers may be used on the track 55.

The wave-shaping circuit 14 of FIG. 1 is shown, schematically, as anexample. Various different types of circuits may be used, for example itis possible to so construct a circuit that the output pulses of coil 13,or of photo cell 58, respectively, are directly converted into squarewave pulses, and the pulses are then fitted, as well known, in twodifferent time slots. In any event, the counting state of the counter 27should be transferred to the storage counter 28 before a new initialnumber is loaded into counter 27 preferably just in advance of a fixedtime effecting such loading.

The circuit, as described, solves the problem initially mentioned.Integrated circuits are used exclusively, operating digitally, so thatno specific matching of analog circuits to specific engines isnecessary. No effects of aging of components will change the operatingcharacteristics. A particular advantage of the circuit of the presentinvention is that it permits consideration of further operating orambient parameters to determine the exact ignition angle, by modifyingeither the counting frequency of the counter 27 (by variation of thefrequency of the oscillator 26), by changing the initial counting stateof counter 27, or by changing the initial counting state of the counter35, that is, three different ways can be used to consider suchadditional parameters when controlling the ignition instant.

The invention has been described with respect to triggering of anignition event. The same circuit may also be used to control theinjection time, or injection instant in fuel injection systems, or tocontrol the opening time and closing time of electro-hydraulicallycontrolled inlet and outlet valves. The function generating markers ontrack 56 of the disk of FIG. 7, or the teeth on star-wheel 31 (FIG. 1respectively, may be suitably distributed to provide suitable functionsto compensate for different characteristics of the desired controlevent, with respect to a predetermined position of a movable element ofthe engine, for example a specific angular position of the crankshaft ofthe engine.

I claim:

1. Digital system to provide a trigger signal to trigger an operatingevent in an operated device at a time subsequent to a datum instant,which time depends on operating conditions of the device,

characterized by a. first transducer means (10) coupled to the deviceand providing a sequence of first pulses representative of an operatingcondition thereof;

first counter means (27, 28) having said first pulses applied thereto,determining the time gap between pulses, and providing a representationof said time gap in form of a digital number;

b. a function generator (30) providing a second sequence of secondpulses, having a time distribution which is representative of thefunction of variation of an operating condition with respect to theoperating condition of said device subsequent to operation with respectto said datum;

second counter means (35) providing a representation of the number ofsecond pulses, derived from said function generator, in the form of asecond digital number, arising subsequent to said datum;

c. a digital comparator (39) connected to and comparing the numbers inboth said first counter means (27, 28) and said second counter means(35) and providing said trigger signal upon determination of equality ofsaid first and second digital number;

d. a start number storage means (41) connected to at least one of saidcounter means (27, 28; 35), and providing a predetermined start numberto the respective counter means representative of an operating conditionof the device; and

e. means (36, 37) coupled to said operated device, providing a datumreference pulse, and providing said pulse at a predetermined operatingposition of an operating element of said device to form said datum, theload input terminal (a) of said second counter means (35) beingcontrolled by the datum reference pulse from said reference pulse sourcemeans.

2. System according to claim 1, wherein said first counter meanscomprises a first counter (27) and a storage counter (28), the

storage counter storing the digital number representative of said timegap, said storage counter being connected to said digital comparator forcomparison of said first digital number with the second digital numberin the second counter (35).

3. System according to claim 1, further comprising a count pulsegenerator means (26) generating a sequence of count pulses having apulse repetition rate (PRR) which is high with respect to the PRR of thesequence of first pulses, said sequence of count pulses being applied tosaid first counter means to determine the binary number stored in saidfirst counter means between successive first pulses applied to saidfirst counter means (27, 28).

4. System according to claim 3, further comprising means (20, 21)sensing an operating condition of the device, said sensing means beingconnected to and controlling the PRR of the count pulse generating means(26) so that the binary number stored in the first counter means will bea function of (a) the time gap between successive pulses and (b) sensedoperating conditions of the device.

5. System according to claim 1, wherein the start number storage meanscomprises at least one start number store (41, 42) having means (43, 44)controlling entry of a number therein;

said at least one start number store being connected to, respectively,at least one of said first and second counter means (27, 28; 35) toprovide an initial number to the respective first and second countermeans for algebraic combination with the number being entered into saidrespective first or second counter means.

6. System according to claim 5, further comprising second transducermeans (45, 46, 47) sensing a condition of operation of said device,connected to said start number store to enter a start number to saidstart number store representative of a condition of operation of saiddevice.

7. System according to claim 1, wherein said device is a mechanicalapparatus having movable elements including a rotatable shaft (38)rotating in synchronism with movement of said elements, and comprisingmeans (36, 37; 54, 57) responsive to a predetermined angular position ofsaid shaft (38) and providing a datum signal, said predetermined angularposition forming said datum, said datum signal being connected to saidsecond counter means (35) to enable the second counter means to counterpulses derived from said function generator (30) upon receipt of saiddatum signal.

8. System according to claim 1, wherein said device is a movableapparatus having a movable element, and wherein the first transducermeans is coupled to said movable element and provides a sequence ofpulses representative of change in position of said movable element sothat the elapsed time between successive pulses will be a measure of thespeed of movement of said element from a first position to a nextsubsequent position.

9. System according to claim 1, wherein the device is a mechanicalapparatus having a rotatable shaft (38), said first transducer means(10) is a speed pulse transducer providing speed signal pulses and saidfunction generator (30) provides a sequence of pulses representative ofangular position of the shaft (38) in accordance with a function havinga non-linear relationship of accumulated pulse count with respect toangular position, said system comprising a disk rotating in synchronismwith said shaft having a first circumferential track (55) carrying marksthereon uniformly spaced about the circumference to provide the speedsignal pulses, a second circumferential track (56) having markersthereon located above the circumference thereof and starting from aposition corresponding to said datum, said markers of said secondcircumferential track being distributed about the circumference of thedisk in accordance with said non-linear function;

and stationary reading means (58, 59) responsive to said markers andproviding a pulse upon passage of a marker before the reading means,said markers on the disk, and said reading means forming, respectively,said transducer and said function generator means.

10. System according to claim 2, wherein the start number storage means(41) has an initial number stored therein representative of an operatingcondition of the device which has a persistence time which is long withrespect to recurrence rate of said pulses;

the first pulse controlling tranfer of the count in the first counter(27) to said storage counter (28) and, immediately thereafter,transferring the count from said start number storage means (41) intosaid first counter (27).

11. System according to claim 10, wherein the start number storagecounter (41) comprises a read-only memory (ROM) (41);

and means (48, 49) applying a digital number to said ROM, the value ofwhich is controlled by conditions of operation of said device.

12. System according to claim 1, further comprising a count pulseoscillator (26) coupled to the device and generating a sequence of countpulses representative of an operating condition of said device otherthan that sensed by said first transducer means (10), connected to thecounting input (2) of said first counter means (27, 28).

13. System according to claim 12, wherein the oscillation frequency ofsaid oscillator is variable and high with respect to said sequence offirst pulses,

14. System according to claim 12, wherein the oscillator (26) is an L/Coscillator having a tank circuit (24, including a variable inductance(24) having a movable core (23), said device comprises an internalcombustion engine, and the position of said core is variable inaccordance with vacuum in the induction system of the engine.

15. System according to claim 14, wherein the core has a conical shape.

16. System according to claim 1, wherein the start number storage means(42) comprises a read-only memory (ROM), and means (46, 47; 45)introducing a start number to said ROM and having a binary valuerepresentative of an operating condition of said device.

17. System according to claim 1, wherein at least one of said countermeans (27; 35) comprises a down counter.

18. System according to claim 5, wherein said device comprises aninternal combustion engine;

a threshold switch (45) is provided, the switching state of saidthreshold switch being determined by the temperature of said internalcombustion engine, said threshold switch being connected to at least oneof said start number storage means to provide an initial number to therespective storage means, the value of which depends on the temperatureof the engine.

19. System according to claim 1, wherein said device comprises arotating engine, said transducer means (10) and said function generator(30) comprising electromagnetic transducers including, each, a starwheel (11, 31) having ferromagnetic teeth, and magnetic pick-up means(13, 33) respectively, magnetically coupled to respective star wheels;

the tooth distribution of the star wheel of the transducer being uniformabout its circumference, and the tooth distribution of the functiongenerator being non-linearly distributed about the circumferencethereof, in accordance with said function.

20. System according to claim 1, wherein said device is an internalcombustion engine, a reference pulse source (36, 37) is providedcomprising a switch (36), opened and closed, periodically, insynchronism with rotation of said engine.

21. System according to claim 1, wherein said device comprises arotating internal combustion engine, and means are provided to generatea reference pulse at a predetermined angular position of the crankshaftof the internal combustion engine;

wherein said first transducer means, said function generator, and saidreference pulse generating means comprises photoelectric transducermeans including a disk having alternatingly occuring opaque andtransparent zones, and photoelectric means sensing the presence of saidrespective zones.

22. System according to claim 21, wherein said disk comprises threeconcentric tracks (54, 55, 56) having opaque markers thereon;

three photoelectric transducer means (57, 58, 59) one, each, associatedwith said tracks, and reading said markers and forming said transducermeans, said function generator means and said reference pulse generatormeans, respectively. 23. Ignition pulse control system for an internalcombustion engine comprising the digital system as claimed in claim 1,wherein said internal combustion engine forms said device and saidtrigger signal provides the ignition control signal therefor;

said first transducer means (10) provides a sequence of pulsesrepresentative of time gap between uniform, predetermined angulardisplacement of the crankshaft of the engine; said first counter means(27, 28) comprises a first counter (27) and a storage counter (28);count pulse generator means (26) are provided coupled to the engine, andproviding count pulses at a repetition rate which is representative ofengine loading, which rate is high with respect to the recurrence rateof said first pulses; the count pulse generator means (26) beingconnected to said first counter (27), said first counter (27) counting acountable number of count pulses in the gaps, or intervals betweenrecurrence of said first pulses, the number of count pulses countedduring said gaps being a function of a. the pulse repetition rate ofsaid count pulses as generated by said count pulse generator means (26)and b. the duration of said gaps, or elapsed time between said firstpulses,

said function generator (30), providing said second sequence of secondpulses being coupled to the crankshaft of the engine and providing saidsecond sequence of pulses at a nonuniform recurrence rate, in dependenceon angular position of the crankshaft of the engine, with respect toupper dead center position of the crankshaft;

said first pulses transferring a counted number in said first counter(27) to said storage counter (28), and said digital comparator (30)comparing the stored number in said storage counter (28) with thecounted number in said second counter means (35) and providing anignition trigger pulse upon sensed coincidence of said numbers.

whereby the comparator will compare a first digital numberrepresentative of a composite of engine speed and loading with a seconddigital number representative of a function of crankshaft position,forming a composite of ignition timing with respect to upper dead centercrankshaft position.

24. System according to claim 23, further comprising at least one startnumber storage means (41, 42) having input terminals (43, 44),respectively, to set a predetermined number into said start numberstorage means;

and means (45, 46, 47; 48; 49) sensing a condition of operation of theengine, connected to a respective input terminal of said at least onestart number storage means to enter a start number thereinrepresentative of a condition of operation of said engine.

25. Digital system to provide a trigger signal to trigger an operatingevent in an operated device at a time subsequent to a datum instant,which time depends on operating conditions of the device,

characterized by I M, J

a. first transducer means coupled to the device and providing a sequenceof first pulses representative of an operating condition thereof;

first counter means (27, 28) having said first pulses applied thereto,determining the time gap between pulses, and providing a representationof said time gap in form of a digital number;

b, a function generator (30) providing a second sequence of secondpulses, having a time distribution which is representative of thefunction of variation of an operating condition with respect to theoperating condition of said device subsequent to operation with respectto said datum;

second counter means (35) providing a representation of the number ofsecond pulses, derived from said function generator, in the form of asecond digital number, arising subsequent to said datum;

c. a digital comparator (39) connected to and comparing the numbers inboth said first counter means (27, 28) and said second counter means(35) and providing said trigger signal upon determination of equality ofsaid first and second digital numbers;

d. and a count pulse oscillator (26) coupled to said operated device andgenerating a sequence of count pulses at a repetition rate which isrepresentative of an operating condition of said device, and at a ratewhich is high with respect to the recurrence rate of said first pulses,the count pulse oscillator (26) being connected to the counting input(2) of said first counter means (27, 28);

whereby the comparator (39) will compare a digital number representativeof a composite of the operating conditions sensed by the firsttransducer means and the count pulse oscillator, with a digital numberrepresentative of a function of a variation of an operating condition ofsaid device subsequent to operation of said device with respect to saiddaturn.

26. Internal combustion engine in ignition trigger pulse control systemto provide a trigger signal to initiate ignition, comprising firsttransducer means (10) coupled to the crankshaft of the engine andproviding a sequence of first pulses representative of speed of engineoperation;

a count pulse generator (26) coupled to the engine and providing countpulses at a repetition rate which is representative of engine loading;

first counter means having said first pulses representative of enginespeed and said count pulses representative of engine loading appliedthereto and counting a digital number, the value of which isrepresentative of engine speed at a certain load;

datum signal generating means (36) providing a signal representative ofa predetermined angular datum crankshaft position in advance of upperdead center position of a piston of the engine;

a function generator (30) providing a second sequence of second pulseshaving a time distribution which is representative of the function ofvariation of ignition timing with respect to instantaneous angularcrankshaft position of the engine with respect to said datum;

second counter means (35) providing a digital count numberrepresentative of the number of second pulses, derived from saidfunction generator, subsequent to the engine crankshaft passing saiddatum angular position;

and a digital comparator (39) connected to and comparing the number inboth said first counter means (27, 28) representative of a composite ofengine speed and engine loading with the number in said second countermeans (35) representative of the function of ignition timing withrespect to instantaneous angular crankshaft position, and providing saidtrigger signal upon determination of a predetermined relationship ofsaid first and second digital numbers.

27. System according to claim 26, further comprising means (46, 47; 48,49) sensing operating conditions of the engine which have a persistencetime which is long with respect to the recurrence time of said first andsecond pulses;

start number storage means (41, 42) connected to said long-timecondition sensing means and controlled thereby, the output of said startnumber storage means (41, 42) being connected to at least one of saidcounter means (27, 28; 35) to provide a predetermined start number tothe respective counter means,

to modify the count in said counter means, for comparison in saidcomparator (39) in accordance with engine operating conditionsindependent'of instantaneous angular crankshaft position of the engine.

1. Digital system to provide a trigger signal to trigger an operatingevent in an operated device at a time subsequent to a datum instant,which Time depends on operating conditions of the device, characterizedby a. first transducer means (10) coupled to the device and providing asequence of first pulses representative of an operating conditionthereof; first counter means (27, 28) having said first pulses appliedthereto, determining the time gap between pulses, and providing arepresentation of said time gap in form of a digital number; b. afunction generator (30) providing a second sequence of second pulses,having a time distribution which is representative of the function ofvariation of an operating condition with respect to the operatingcondition of said device subsequent to operation with respect to saiddatum; second counter means (35) providing a representation of thenumber of second pulses, derived from said function generator, in theform of a second digital number, arising subsequent to said datum; c. adigital comparator (39) connected to and comparing the numbers in bothsaid first counter means (27, 28) and said second counter means (35) andproviding said trigger signal upon determination of equality of saidfirst and second digital number; d. a start number storage means (41)connected to at least one of said counter means (27, 28; 35), andproviding a predetermined start number to the respective counter meansrepresentative of an operating condition of the device; and e. means(36, 37) coupled to said operated device, providing a datum referencepulse, and providing said pulse at a predetermined operating position ofan operating element of said device to form said datum, the load inputterminal (a) of said second counter means (35) being controlled by thedatum reference pulse from said reference pulse source means.
 2. Systemaccording to claim 1, wherein said first counter means comprises a firstcounter (27) and a storage counter (28), the storage counter storing thedigital number representative of said time gap, said storage counterbeing connected to said digital comparator for comparison of said firstdigital number with the second digital number in the second counter(35).
 3. System according to claim 1, further comprising a count pulsegenerator means (26) generating a sequence of count pulses having apulse repetition rate (PRR) which is high with respect to the PRR of thesequence of first pulses, said sequence of count pulses being applied tosaid first counter means to determine the binary number stored in saidfirst counter means between successive first pulses applied to saidfirst counter means (27, 28).
 4. System according to claim 3, furthercomprising means (20, 21) sensing an operating condition of the device,said sensing means being connected to and controlling the PRR of thecount pulse generating means (26) so that the binary number stored inthe first counter means will be a function of (a) the time gap betweensuccessive pulses and (b) sensed operating conditions of the device. 5.System according to claim 1, wherein the start number storage meanscomprises at least one start number store (41, 42) having means (43, 44)controlling entry of a number therein; said at least one start numberstore being connected to, respectively, at least one of said first andsecond counter means (27, 28; 35) to provide an initial number to therespective first and second counter means for algebraic combination withthe number being entered into said respective first or second countermeans.
 6. System according to claim 5, further comprising secondtransducer means (45, 46, 47) sensing a condition of operation of saiddevice, connected to said start number store to enter a start number tosaid start number store representative of a condition of operation ofsaid device.
 7. System according to claim 1, wherein said device is amechanical apparatus having movable elements including a rotatable shaft(38) rotating in synchronism with movement of said elements, andcomprising means (36, 37; 54, 57) responsive tO a predetermined angularposition of said shaft (38) and providing a datum signal, saidpredetermined angular position forming said datum, said datum signalbeing connected to said second counter means (35) to enable the secondcounter means to counter pulses derived from said function generator(30) upon receipt of said datum signal.
 8. System according to claim 1,wherein said device is a movable apparatus having a movable element, andwherein the first transducer means is coupled to said movable elementand provides a sequence of pulses representative of change in positionof said movable element so that the elapsed time between successivepulses will be a measure of the speed of movement of said element from afirst position to a next subsequent position.
 9. System according toclaim 1, wherein the device is a mechanical apparatus having a rotatableshaft (38), said first transducer means (10) is a speed pulse transducerproviding speed signal pulses and said function generator (30) providesa sequence of pulses representative of angular position of the shaft(38) in accordance with a function having a non-linear relationship ofaccumulated pulse count with respect to angular position, said systemcomprising a disk rotating in synchronism with said shaft having a firstcircumferential track (55) carrying marks thereon uniformly spaced aboutthe circumference to provide the speed signal pulses, a secondcircumferential track (56) having markers thereon located above thecircumference thereof and starting from a position corresponding to saiddatum, said markers of said second circumferential track beingdistributed about the circumference of the disk in accordance with saidnon-linear function; and stationary reading means (58, 59) responsive tosaid markers and providing a pulse upon passage of a marker before thereading means, said markers on the disk, and said reading means forming,respectively, said transducer and said function generator means. 10.System according to claim 2, wherein the start number storage means (41)has an initial number stored therein representative of an operatingcondition of the device which has a persistence time which is long withrespect to recurrence rate of said pulses; the first pulse controllingtranfer of the count in the first counter (27) to said storage counter(28) and, immediately thereafter, transferring the count from said startnumber storage means (41) into said first counter (27).
 11. Systemaccording to claim 10, wherein the start number storage counter (41)comprises a read-only memory (ROM) (41); and means (48, 49) applying adigital number to said ROM, the value of which is controlled byconditions of operation of said device.
 12. System according to claim 1,further comprising a count pulse oscillator (26) coupled to the deviceand generating a sequence of count pulses representative of an operatingcondition of said device other than that sensed by said first transducermeans (10), connected to the counting input (z) of said first countermeans (27, 28).
 13. System according to claim 12, wherein theoscillation frequency of said oscillator is variable and high withrespect to said sequence of first pulses.
 14. System according to claim12, wherein the oscillator (26) is an L/C oscillator having a tankcircuit (24, 25) including a variable inductance (24) having a movablecore (23), said device comprises an internal combustion engine, and theposition of said core is variable in accordance with vacuum in theinduction system of the engine.
 15. System according to claim 14,wherein the core has a conical shape.
 16. System according to claim 1,wherein the start number storage means (42) comprises a read-only memory(ROM), and means (46, 47; 45) introducing a start number to said ROM andhaving a binary value representative of an operating condition of saiddevice.
 17. System according to claim 1, wherein at least one of saidcounter means (27; 35) comprises A down counter.
 18. System according toclaim 5, wherein said device comprises an internal combustion engine; athreshold switch (45) is provided, the switching state of said thresholdswitch being determined by the temperature of said internal combustionengine, said threshold switch being connected to at least one of saidstart number storage means to provide an initial number to therespective storage means, the value of which depends on the temperatureof the engine.
 19. System according to claim 1, wherein said devicecomprises a rotating engine, said transducer means (10) and saidfunction generator (30) comprising electromagnetic transducersincluding, each, a star wheel (11, 31) having ferromagnetic teeth, andmagnetic pick-up means (13, 33) respectively, magnetically coupled torespective star wheels; the tooth distribution of the star wheel of thetransducer being uniform about its circumference, and the toothdistribution of the function generator being non-linearly distributedabout the circumference thereof, in accordance with said function. 20.System according to claim 1, wherein said device is an internalcombustion engine, a reference pulse source (36, 37) is providedcomprising a switch (36), opened and closed, periodically, insynchronism with rotation of said engine.
 21. System according to claim1, wherein said device comprises a rotating internal combustion engine,and means are provided to generate a reference pulse at a predeterminedangular position of the crankshaft of the internal combustion engine;wherein said first transducer means, said function generator, and saidreference pulse generating means comprises photoelectric transducermeans including a disk having alternatingly occuring opaque andtransparent zones, and photoelectric means sensing the presence of saidrespective zones.
 22. System according to claim 21, wherein said diskcomprises three concentric tracks (54, 55, 56) having opaque markersthereon; three photoelectric transducer means (57, 58, 59) one, each,associated with said tracks, and reading said markers and forming saidtransducer means, said function generator means and said reference pulsegenerator means, respectively.
 23. Ignition pulse control system for aninternal combustion engine comprising the digital system as claimed inclaim 1, wherein said internal combustion engine forms said device andsaid trigger signal provides the ignition control signal therefor; saidfirst transducer means (10) provides a sequence of pulses representativeof time gap between uniform, predetermined angular displacement of thecrankshaft of the engine; said first counter means (27, 28) comprises afirst counter (27) and a storage counter (28); count pulse generatormeans (26) are provided coupled to the engine, and providing countpulses at a repetition rate which is representative of engine loading,which rate is high with respect to the recurrence rate of said firstpulses; the count pulse generator means (26) being connected to saidfirst counter (27), said first counter (27) counting a countable numberof count pulses in the gaps, or intervals between recurrence of saidfirst pulses, the number of count pulses counted during said gaps beinga function of a. the pulse repetition rate of said count pulses asgenerated by said count pulse generator means (26) and b. the durationof said gaps, or elapsed time between said first pulses, said functiongenerator (30), providing said second sequence of second pulses beingcoupled to the crankshaft of the engine and providing said secondsequence of pulses at a nonuniform recurrence rate, in dependence onangular position of the crankshaft of the engine, with respect to upperdead center position of the crankshaft; said first pulses transferring acounted number in said first counter (27) to said storage counter (28),and said digital comparator (30) comparing the stored number in saidstorage counter (28) witH the counted number in said second countermeans (35) and providing an ignition trigger pulse upon sensedcoincidence of said numbers, whereby the comparator will compare a firstdigital number representative of a composite of engine speed and loadingwith a second digital number representative of a function of crankshaftposition, forming a composite of ignition timing with respect to upperdead center crankshaft position.
 24. System according to claim 23,further comprising at least one start number storage means (41, 42)having input terminals (43, 44), respectively, to set a predeterminednumber into said start number storage means; and means (45, 46, 47; 48;49) sensing a condition of operation of the engine, connected to arespective input terminal of said at least one start number storagemeans to enter a start number therein representative of a condition ofoperation of said engine.
 25. Digital system to provide a trigger signalto trigger an operating event in an operated device at a time subsequentto a datum instant, which time depends on operating conditions of thedevice, characterized by a. first transducer means (10) coupled to thedevice and providing a sequence of first pulses representative of anoperating condition thereof; first counter means (27, 28) having saidfirst pulses applied thereto, determining the time gap between pulses,and providing a representation of said time gap in form of a digitalnumber; b. a function generator (30) providing a second sequence ofsecond pulses, having a time distribution which is representative of thefunction of variation of an operating condition with respect to theoperating condition of said device subsequent to operation with respectto said datum; second counter means (35) providing a representation ofthe number of second pulses, derived from said function generator, inthe form of a second digital number, arising subsequent to said datum;c. a digital comparator (39) connected to and comparing the numbers inboth said first counter means (27, 28) and said second counter means(35) and providing said trigger signal upon determination of equality ofsaid first and second digital numbers; d. and a count pulse oscillator(26) coupled to said operated device and generating a sequence of countpulses at a repetition rate which is representative of an operatingcondition of said device, and at a rate which is high with respect tothe recurrence rate of said first pulses, the count pulse oscillator(26) being connected to the counting input (z) of said first countermeans (27, 28); whereby the comparator (39) will compare a digitalnumber representative of a composite of the operating conditions sensedby the first transducer means and the count pulse oscillator, with adigital number representative of a function of a variation of anoperating condition of said device subsequent to operation of saiddevice with respect to said datum.
 26. Internal combustion engine inignition trigger pulse control system to provide a trigger signal toinitiate ignition, comprising first transducer means (10) coupled to thecrankshaft of the engine and providing a sequence of first pulsesrepresentative of speed of engine operation; a count pulse generator(26) coupled to the engine and providing count pulses at a repetitionrate which is representative of engine loading; first counter meanshaving said first pulses representative of engine speed and said countpulses representative of engine loading applied thereto and counting adigital number, the value of which is representative of engine speed ata certain load; datum signal generating means (36) providing a signalrepresentative of a predetermined angular datum crankshaft position inadvance of upper dead center position of a piston of the engine; afunction generator (30) providing a second sequence of second pulseshaving a time distribution which is representative of the function ofvarIation of ignition timing with respect to instantaneous angularcrankshaft position of the engine with respect to said datum; secondcounter means (35) providing a digital count number representative ofthe number of second pulses, derived from said function generator,subsequent to the engine crankshaft passing said datum angular position;and a digital comparator (39) connected to and comparing the number inboth said first counter means (27, 28) representative of a composite ofengine speed and engine loading with the number in said second countermeans (35) representative of the function of ignition timing withrespect to instantaneous angular crankshaft position, and providing saidtrigger signal upon determination of a predetermined relationship ofsaid first and second digital numbers.
 27. System according to claim 26,further comprising means (46, 47; 48, 49) sensing operating conditionsof the engine which have a persistence time which is long with respectto the recurrence time of said first and second pulses; start numberstorage means (41, 42) connected to said long-time condition sensingmeans and controlled thereby, the output of said start number storagemeans (41, 42) being connected to at least one of said counter means(27, 28; 35) to provide a predetermined start number to the respectivecounter means, to modify the count in said counter means, for comparisonin said comparator (39) in accordance with engine operating conditionsindependent of instantaneous angular crankshaft position of the engine.